A 53-year-old male undergoing emergency aortic valve replacement for infective endocarditis developed a hypertensive crisis early during the operation. Suspecting a pheochromocytoma, intravenous phentolamine was immediately administered, after which the procedure was completed as scheduled. Although quite rare, a pheochromocytoma can be encountered during emergency open heart surgery, thus early recognition of abnormal blood pressure change and appropriate management are important. Here, we present details of blood pressure control mainly by phentolamine use in this case to demonstrate effective management of a hypertensive crisis during emergency cardiac surgery because of a pheochromocytoma.